You won’t like the answer, but succinctly: you don’t.
Skritter changed. The new mobile app follows a different paradigm than the old Skritter app (or website).
Skritter does not automatically add words. You don’t mark lists as “being studied”.
Instead, Skritter teaches you words by walking through a lesson for each new word you manually choose to add. You can learn from any list, any time, in any order.
After you say you want to learn a word, you’ll have the option to say it’s already learned, and Skritter will not take you through the teaching cycle, but will add it directly to your SRS queue.
So, you will need to go into your list, and “learn” words. Currently that is a “one-by-one” process. And my experience is if you try to do it too fast, the Skritter database has problems keeping up and doesn’t really add the words (you come back into Skritter later and find words you marked as learned as not marked that way).